Bearings such as rolling bearings are used in all types of mechanical applications to reduce friction between moving parts. Rolling bearings provide low friction rotation by means of rolling elements arranged between an inner and an outer race. In order to reduce friction and wear between the rolling elements and the races, a bearing lubricant such as grease or oil is often used.
It has been found that bearing failures are often caused by water in the lubricant. Water in the lubricant can cause surface erosion and cavitations within the bearing as well as hydrogen embrittlement due to the extreme pressures in rolling element bearings. These may reach levels as high as 1 to 3 GPa, where water can disassociate into its constituent atoms. Free hydrogen atoms may then penetrate through the surfaces of the bearing components and make them brittle. Water also speeds up the oxidization of base oil and can cause additives to precipitate and form abrasive particles or sludge. Even in situations where there is no water entering the bearing from the outside, the water content in the lubricant may increase slightly due to oxidation of hydrocarbons in the lubricant.
The risk of unexpected bearing failures may be reduced by using a sensor that monitor the water content in the lubricant or some other parameter such as the temperature or pressure of the lubricant. Despite the efforts that have gone into developing such sensors, many of the systems that are currently available are often complicated and impractical to use in many application. There is thus a need for further development in this area.